The present invention relates generally to diesel engine systems of the type that incorporate a turbocharger to supply compressed air to a diesel engine, and more particularly to apparatus for monitoring certain of the more critical operating parameters of the system and for effecting control over the system in the event the monitored operating parameters exceed certain predetermined operating limits.
In large-bore, high-horsepower diesel engines of the type to which the present invention is directed, the greater amount of fuel required to operate the engine necessitates a proportionately greater amount of combustion air in order to burn the fuel. Thus, in larger diesel engines where high horsepower is demanded, some form of air supply is needed. This need is met by the utilization of a turbocharger that operates to pump the additional air for the engine, and thereby increase substantially the engine's efficiency and horsepower. In diesel engine systems today, the turbocharger is designed to operate from the exhaust gases produced by the diesel engines. The turbocharger is constructed with an exhaust-driven turbine connected to an air impeller that functions to produce the supply of combustion air for the engine.
In two-cycle engines, exhaust-driven turbochargers lose their efficiency at intermediate to low speeds, necessitating an assist from the engine through a gear train. Thus, at initial (i.e., start-up) speeds, the engine directly drives the impeller to develop the supply of combustion air. As engine RPM increases, the energy contained in the exhaust gases of the engine also increases, and a point is reached whereby the engine's exhaust gas energy is capable of driving the turbine/impeller combination at a speed that will provide adequate combustion air, and without the gear-driven assistance of the engine. At this point, the engine is decoupled from the impeller by an overriding clutch, and the impeller allowed to overrun.
While such large-bore diesel engine systems as described achieve extremely high horsepower ratings, the systems are prone to certain failures. One of the principal sources of failure is overspeed of the rotor assembly; that is, the turbine/impeller combination is rotated at revolutions per minute (RPM), higher than that at which the turbocharger is designed. Turbocharger overspeeding can be caused by a number of factors, including fires in the exhaust manifolds of the diesel engine, creating additional energy that will overspeed the turbocharger. Further, failure of the overriding clutch (in two-cycle engines) to properly disengage will damage the turbocharger if permitted to go undetected.
If these conditions are left to exist for too long a period, the turbocharger will ultimately destroy itself.
Further, diesel engine systems are often designed as a unit; that is, the turbocharger is designed to meet the specific rated horsepower requirements of the diesel engine. Often, unfortunately, after the engine and turbocharger have been so designed and put in use, the engine is reworked to increase its horsepower rating by various modifications, such as increasing the engine bore, increasing piston stroke, increasing the compression ratio, or other known modifications. Thus, the diesel engine horsepower rating may be increased beyond original specifications by these modifications by as much as 50% to 75%; yet a turbocharger that is designed for a lower horsepower rating is often still being used with the higher horsepower engine. It is when this happens that the overspeed situations can become more prevalent.
In addition to failures caused by overspeeding the turbocharger, other failures that cause near-total, if not total, destruction of the turbocharger include bearing wear that, if undetected, will reach a point permitting the turbocharger to literally tear itself apart at the high RPM of normal operation; loss of oil pressure; and similar malfunctions.
Thus there is a need for a system capable of monitoring the turbocharger and large-bore diesel engine assembly to detect when certain operating parameters, such as the temperature of the exhaust gases, failure of the overriding clutch to release at its release point, oil pressure, movement of the shaft carrying the turbine and compressor, and the like to ensure that the turbocharger does not exceed certain predefined limits and, if it does, to control the system to avoid destruction.